Wafer bonding is a microelectromechanical (MEMS), nanoelectromechanical (NEMS), microelectronic, and/or optoelectronic packaging technology for mechanically stable and hermetically sealed device encapsulation. A number of wafer bonding techniques have been developed, including adhesive bonding, anodic bonding, direct bonding, direct metal-to-metal bonding, eutectic bonding, low-temperature melting glass bonding, solder bonding, thermocompression bonding, and ultrasonic bonding. With respect to the foregoing wafer bonding techniques, adhesive wafer bonding is advantageous in that it is a relatively low-temperature technique that does not require application of an electric voltage or current. As such, adhesive wafer bonding may be applied to a wide variety of substrates that are sensitive to temperature and/or the application of electric voltage or current, and is important in integrated circuit (IC) packaging concepts, such as Wafer Level Packaging (WLP), System in Package (SiP), and three-dimensional (3D) integration.
Adhesive wafer bonding is commonly performed by applying an organic adhesive on one or both substrates using a spin-on or spray-on technique. Such a technique requires that the adhesive be dissolved in a solvent, examples being SU-8, SU-8 2000, Polyimide, and BCB, three commonly used adhesives in adhesive wafer bonding, dissolved in gamma butyrolactone, cyclopentanone, and xylene respectively. Application of the foregoing solvent-based, organic adhesives has a significant drawback when it comes to three-dimensional and other non-planar substrates, namely a lack of adequate control resulting in uneven distribution of the adhesive, issues with outgassing of solvents, and delamination and wrinkling upon solvent bake/annealing.
Citation or identification of any reference in Section 2, or in any other section of this application, shall not be considered an admission that such reference is available as prior art to the present invention.